The present invention relates to a method for producing stabilized and highly activated platinum colloid, and highly activated platinum colloid produced by the same method.
The method for producing metallic colloid is largely classified into a physical method and a chemical method. The physical method is called a xe2x80x9cburning methodxe2x80x9d. In the burning method, a metallic ion solution is inputted into a hydrogen gas or phosphor to perform a reduction reaction, and thereafter the solution is heated by burning to foster the reaction, whereby generated metallic corpuscles are received in a liquid dispersion medium, and, after the reduction is completed, the metallic colloid is treated to be well stabilized, using a surface-active agent.
Contrarily, the chemical method is called a xe2x80x9cdeposition methodxe2x80x9d (metallic salt reduction reaction method). The chemical method is such that, after metal oxide and metal deposition are generated from a metallic ion solution, by utilizing a chemical reaction, a surface-active agent is doped to obtain metallic colloid.
However, when using the burning method, metallic corpuscles are precipitated in a burner, and the jetting portion of the burner is clogged due to precipitated metallic particles, wherein there is a problem or a shortcoming in that the burner cannot be used for a long period.
On the contrary, in the deposition method, by precious metal salt being reduced and treated in a water solution under the existence of a surface-active agent, precious metal hydrosol or precious metal sol, which is metallic colloid, is generated (Japanese Laid-Open Patent Application No. 12024 of 1984, Prior art (1)). The deposition method is a more rational method than the burning method.
However, in the prior art deposition method, metallic hydrosol of high concentration cannot be obtained in a water solution. The reason is not necessarily made clear. It seems that a problem resides in the treatment method.
In order to solve these problems, Japanese Laid-Open Patent Application No. 68008 of 1998 (Method for producing high activated metallic corpuscles) (Prior art (2)) proposed a method for stabilizing the colloid state of metallic colloid by reducing and reacting metallic ions, without always depending on a surface-active agent.
That is, the method of the prior art (2) is a method for producing highly activated metallic corpuscles, by which metallic corpuscles are precipitated in a metallic ion solution by treating and reducing the solution with a reducing agent doped to the solution while controlling the temperature and pH. The temperature of the solution is usually controlled at a higher temperature while being in a range from 20xc2x0 C. through 80xc2x0 C. during the reaction, and the pH is kept in a range from 4 through 11, wherein the reduction treatment does not depend on any surface-active agent (protective colloid), and the metallic ions are reduced to be kept in a colloid state.
Also, when using a surface-active agent, it was doped for only the purpose of suppressing the excessive growth of metallic corpuscles precipitated from the surface-active agent.
However, when using the method of the prior art (2), the amount of metallic colloid that can be generated is not quantitative, there is still a shortcoming in that the production loss is considerable. Also, the obtained metallic colloid itself is not stable. It may be liable to become flocculated. Therefore, it was difficult to produce metallic colloid of high concentration in a stabilized manner.
It is considered that there is a large misunderstanding in that, although a surface-active agent is used in a conventional production method using the deposition method, the surface-active agent (protective colloid) has been regarded to prevent the produced metal from becoming flocculated or to deflocculate the same in the conventional method.
It is therefore an object of the invention to provide a method for producing metallic colloid, by which metallic colloid of high concentration can be obtained while using the conventional deposition method in which a metallic ion solution is reduced and treated in a liquid dispersion medium.
In order to achieve the object, a method for producing metallic, i.e. platinum, colloid according to the invention is a method for producing metallic colloid by reducing metallic ions by agitating a treatment solution, in which a surface-active agent is added to water and to which a metallic ion solution and a pH compensating agent are doped, while controlling the temperature of the treatment solution, under a reductive atmosphere,
wherein in a case where water is used with a capacity ratio of 400 through 500 parts with respect to a metallic ion solution whose capacity is 1 part, the surface-active ion solution is a non-ion based surface-active agent, the amount of doping of the non-ion surface-active agent is 0.2 through 2 times with respect to that of the metallic ion solution, the amount of doping of a reducing agent is 40 through 60 times with respect to that of the metallic ion solution, and the pH compensating agent is to adjust the pH of the treatment solution to neutral or weak alkalinity, wherein the amount of doping of the pH compensating agent is set in a range from 10 through 30 times with respect to that of the metallic ion solution if the concentration thereof is 5%.
Also, the pH compensating agent and metallic ion solution are simultaneously doped into the treatment solution.
In addition, the reducing agent is to foster the reduction and reaction of the metallic ion solution. After the reducing agent is doped to the treatment solution and a reductive atmosphere is formed in the treatment solution, the temperature of the treatment solution is further raised, and after the temperature reaches a fixed temperature level, the metallic ion solution and pH compensating agent are doped.
Further, the reducing agent is to foster the reduction and reaction of the metallic ion solution. After the temperature of the treatment solution is raised and reaches a fixed temperature level, the metallic ion solution and pH compensating agent are doped. After that, by doping the reducing agent, a reductive atmosphere is formed in the treatment solution.
Further, the metallic colloid according to the invention is a metallic colloid produced by the method for producing metallic colloid, where the metallic colloid is platinum colloid, ethanol is used as the reducing agent, polysorbate 80 is used as the surface-active agent, a platinum chloride acid solution is used as the metallic ion solution, and sodium bicarbonate is used as the pH compensating agent, and the oxidization reduction potential shows 400 mV or more in the form of a negative value.